The present invention relates to a filter pack for and/or liquid filtration employing filter medium surfaces disposed between pairs of spacers, with the spacers having a corrugated shape and the edges of the corrugations of each spacer being preferably mutually parallel.
A similar filter pack is disclosed in DE-OS No. 2,557,444 corresponding to U.S. Pat. No. 3,941,571. The prior art filter pack is composed of a flow-through housing holding a pleated filter or filter medium surface which is adapted to the cross section of the housing. The pleated filter is composed of a strip which is folded back and forth in a meandering pattern over a plurality of its length sections. A pleat spacer is inserted into each pleat. Each spacer is provided with a plurality of generally parallel double-sided corrugations or pleats.
However, it is also desirable to ensure the filtering of, e.g., suspended matter out of streams of air or gas with a very high degree of separation (.eta..gtoreq.99.97%) also under extreme operating conditions such as increased temperatures, high humidity and high differential pressure. The configuration of the prior art filter pack does not assure meeting this requirement since under stress, for example due to increased differential pressure and possibly in conjunction with high humidity, the pleated filter can tear open. This happens particularly in the arc regions of the meander of the filter medium surface.
Tests have shown that loosening of the filter pack and bulging of individual pleats are two fo the most significant causes of damage. The reason for this is the uncoordinated installation of the individual pleated spacers. During filtering, this causes that either the forces from the pre-tensioned frame and/or the forces from the differential pressure be substantially conducted over the filter medium. As such, if the differential pressure rises under conditions of high humidity and temperature the filter medium is then permanently stretched. This reduces its prior tension and loosens the packed pleats.
On the other hand, excessive pressure results in the deformation of the filter medium and in the development of play between the spacers and the filter medium. As a consequence of this, lateral displacement of the pleats can easily ensue which causes individual pleats to bulge out.